Redox-active ion exchange resin beads have applications in various areas, particularly in synthesis of organic and inorganic compounds via liquid-solid reaction mixtures. Among other advantages, the solid resin reagent is easily filtered from the heterogeneous reaction mixture or the resin can be packed in a cartridge and the other reagents passed through the cartridge.
Halogens can be bound to a resin in a trihalide form; however, resins in a trihalide form have been prepared, though with varying degrees of efficiency. For example, the traditional production of a tribromide resin, Beauman et al., U.S. Pat. No. 4,594,361, is accomplished by conversion of resin in a chloride form to the bromide form by use of large volumes of bromide salt solution. This process generates a large amount of waste mixed salt solution because the displacement of chloride, while favored, is not displaced efficiently by bromide. Subsequently, bromine is added using a large volume of aqueous solution due to bromine's limited solubility in water. Richardson et al., U.S. Pat. No. 7,964,138 teaches conversion of a prototypical macroreticular resin (e.g. Amberlite® IRA-900) into Br3− (resin), which has been extended to gel-type (e.g., Marathon® A) resins.
Chlorine appears to have been bound to resins in the iodide form as ICl2−, which can serve as a source of chlorine, Hatch, U.S. Pat. No. 4,190,529, for addition reactions, but the reactions suffer with the problem of generating iodine addition products as an impurity of the chlorine addition products. The synthesis and properties of resins in a trichloride form are not known.
Chlorine is produced industrially for many uses, including plastics, basic chemicals, refrigerant gases, solvents, pharmaceuticals and as a disinfectant for water treatment. Chlorine gas is extremely toxic and its release can create a significant public health hazard. For this reason, absorbing chlorine on a solid support in a reversible manner such that it can be handled at a reduced risk yet be useful in an efficient manner is desirable. Various materials and chemicals adsorb chlorine gas; however, most absorb Cl2 irreversibly. The most commonly encountered absorbents are zeolites and materials that are destructive of chlorine, such as alumina and activated carbon. Reversible solid chemisorbents, in which the gas can be adsorbed, or absorbed and removed, are not widely reported in the literature, although the use of an amine resin to provide Cl2 and to permit release on demand has been reported, Wayman et al., J. Can. J. Chem. Eng. 1968, 46, 282.
A few salts of trichloride anion, Cl3−, have been shown to serve as Cl2 sources. The equilibrium formation of trichloride ion in aqueous solution is well known by the reaction:Cl−(aq)+Cl2=Cl3−(aq).  (1)
The equilibrium constant for this reaction is 0.18 M−1, so, in dilute solution, Cl2 will be 50% in the form of Cl3− in a solution that is approximately 1/0.18=5.6 M in chloride ion. Trichloride ion can be stabilized in a solid resin free salt by using an appropriate counterion, as disclosed, for example, in Chattaway et al., J Chem Soc 1923, 123, 654, and Schlama et al., Angew. Chem.-Int. Edit. Engl. 1997, 36, 2342. Stable polymeric resins in the trichloride form have not been reported and chloride-form resins have not been used as reversible chlorine chemisorbents. Typical standard anion exchange resins in the chloride form have low affinity of chlorine via the equation:Cl−(res)+Cl2=Cl3−(res).  (2)
For this reason Cl3− bound resins that reversibly bind chlorine for use in a relatively safe method for delivering chlorine have not been publically disclosed and there remains a need for an effective and efficient method of preparing trihalide resins and, particularly, a trichloride resin.